1. Field of the Invention
This invention relates to magnetic tape drives and more particularly relates to detecting the formation of a short between a magnetoresistive (“MR”) head and a head substrate.
2. Description of the Related Art
Prior to the advent of automation technology for linear tape drives, large, open tape reels were manually loaded by operators of tape storage systems. As advances in tape cassette and other technologies were adapted to magnetic tapes drives, large automated tape systems became possible. In such a system, magnetic tape cassettes are automatically selected from a library of tape cassettes, and loaded to and unloaded from magnetic tape drives by a robotic arm or other similar automation technology.
The use of tape cassettes coincided with the introduction of magnetoresistive (MR) thin film heads, which are fabricated using processes similar to those used for hard disk drive heads. Both tape and hard disk drive heads are fabricated on ceramic wafer substrates. The preferred wafer material is aluminum oxide-titanium carbide, which is very hard and also happens to be electrically conductive. In a tape drive, tape contacts the conductive substrate. To avoid adverse tribological process, the substrate may be biased to a preferred voltage level, generally between 0 and 3 volts. Debris from the tape or the environment may collect on the head and electrically bridge the insulation gap between the conductive wafer substrate and the MR heads. The resulting shorting can disrupt the flow of bias current in the MR heads, which is necessary for their proper functioning. The shorting can also disrupt the substrate voltage biasing, leading to further degradation on the surface of the head.
Thus, debris or contamination of the MR heads may result in a short circuit between the MR head element and the head substrate. A typical short will result in increased read errors, or complete failure to read data to the tape. Because of the rubbing of tape on the heads, shorting related errors are generally more likely to occur in tape drives than in hard disk drives and other types of data storage devices.
Current magnetic tape storage systems do not provide a proactive method for identifying substrate-sensor related shorts. Typically, the formation of the short goes unnoticed until either read error rates become excessive or the tape drive fails to read data. Substrate-sensor shorts may be correctable at the time of discovery, but the required head cleaning process is often time consuming and disruptive to normal operation of the tape drive system.
For example, in an automated tape drive system, a short may be detected by an increased error rate while writing data to a tape cassette. In such an example, the automated system must dedicate resources to remove the magnetic tape cassette from the tape drive, insert a head cleaning cassette, allow the cleaning cassette to clean the MR heads, remove the head cleaning cassette, and replace the magnetic tape cassette. This process is often repeated until data can be accurately read or written to the tape.
As a consequence of the cumbersome head cleaning process, data reliability can be negatively impacted, time and system resources are wasted, and system down time is not efficiently used. It would be useful to provide a solution for early detection of shorts between MR heads and the head substrate. Such a solution would reduce error rates, increase efficiency, and better utilize system down time.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for detecting the formation of a short between a MR head and a head substrate. Beneficially, such an apparatus, system, and method would reduce read errors on the magnetic tape storage system, the time and resources required to recover from such errors, and allow for preventative measures to obviate short related failures of tape drive systems.